1. Field of the Invention
This invention relates, in general, to storage amplifiers and more particularly to an amplifier that stores the peak voltage of a changing waveform.
2. Background Art
Systems having a bubble memory require a sense amplifier that converts the information stored magnetically in the bubble memory to a signal compatible with TTL circuitry. The bubbles are rotated through a magneto-resistive detector element. This detector element changes value when a magnetic domain, or bubble, passes underneath it. Since a constant current is being pulled through the detector, the changing resistance produces a voltage waveform. This waveform is supplied to the sense amplifier which converts the information to a digital signal.
Typically, sense amplifiers include a sample and hold circuit for storing the peak magnitude of the waveform for both the presence and absence of a bubble. The stored peak insures the proper voltage is "read" when interrogated.
Sample and hold circuits typically have a differential amplifier responsive to an input signal, and an output signal supplied to an NPN transistor that charges a storage capacitor through its emitter. Although this configuration is relatively fast, it introduces an error term when transition to the hold mode takes place. The base-emitter junction of the NPN transistor is reversed biased, thereby removing a charge quantity from the storage capacitor.
Another known configuration charges the storage capacitor through the collector of an NPN transistor while restricting the base swing. However, in this configuration a capacitor must switch from a coupling mode to an initialing mode, thereby producing spikes in the output. Both of these configurations have a small resolution between a "one" and a "zero", or the presence and absence of a bubble.
Thus, what is needed is a peak storage amplifier that reduces the discharge of a storage capacitor due to inherent characteristics of the circuit and reduces the response to noise.